MATURATION OF HEPATOSOMAL MONOOXYGENATION AND GLUCURONIDATION ACTIVITIES IN PRE-TERM AND FULL-TERM INFANTS AS STUDIED USING THE [N-15]METHACETIN URINE TEST

The non-distressing [N-15]methacetin liver function test was modified and applied to newborn healthy infants in order to measure both the to tal [N-15]methacetin metabolites excreted in the urine (total eliminat ion capacity) and the proportion of glucuronated metabolite. By studyi ng pre-and full-term normotrophic neonates 3-168 days old, the age-dep endent maturation of the two developing liver function processes can b e compared on the basis of either postnatal or postmenstrual age. When solely considering postnatal age, no significant differences between the pre-and full-term infants were observed in the development of the total elimination capacity. However, when postmenstrual age was consid ered, it became apparent that this development starts earlier in pre-t erm infants and continues at the same rate as their full-term counterp arts, up to the postmenstrual age of approximately 280 days. This incr ease subsequently diminishes in the pre-terms. In the same study group , the proportion of glucuronidation, another indicator of the hepatic detoxification system, appears to develop at a lower rate in pre-term than in full-term infants. When postmenstrual age is taken into consid eration, glucuronidation development is also observed to begin earlier in pre-term infants and the slower maturation is more pronounced. Alt hough these results are not generally applicable, they contribute to a better interpretation of the [N-15]methacetin liver function test-for instance when estimating effects due to environmental exposure or acc urately calculating age-related drug dosage for neonates.